Several processes have been disclosed in the prior art for the economical recovery of relatively pure, recyclable glass from municipal trash. Notable examples include U.S. Pat. Nos. 3,650,896; 3,720,380; 3,817,458; application for United States Letters Patent Ser. No. 603,868 filed Aug. 11, 1975; and the article "Glass Recovery From Municipal Trash By Froth Flotation" by Morey et al published in the Proceedings of the Third Mineral Waste Utilization Symposium.
These processes are generally part of an overall system for the treatment of solid waste for recovery and recycle back to the economy of useful values in the waste. The systems usually involve separating organic materials from the inorganic metals, concrete, bricks, and glass, etc. and then further segregating and enriching the individual constituents. The predominantly organic fraction is further segregated to recover saleable materials such as paper pulp and the remainer is either pyrolysized to form char and an economically valuable gaseous stream, or otherwise treated to form a solid fuel, compost, or landfill. The predominantly inorganic fraction is further treated to segregate the ferrous metals, non-ferrous conductive metals, and glass.
An exemplary glass recovery process involves three steps: (1) passing the glass-rich fraction to a first classification zone, such as a screw classifier or jig concentrator, to remove any remaining organic constituents; (2) a second step of size classification, such as by screening or a spiral classifier, preferably in conjunction with the commminution to obtain a preselected size distribution of the organic-free glass; and, (3) froth flotation to separate the glass from the other inorganic tailings. Processes of this type use a considerable amount of water. For example, the process described in application for United States Letters Patent Ser. No. 603,868 utilizes approximately 10,000 gallons of water to recover each ton of glass. Heretofore, this water, after use in the various aspects of the process, was discharged to the sewer. This is because the several attempts that have been made to centrally treat the water used in the process, to thereby place it in condition for reuse, have either been more expensive per gallon of fresh water or, for the most part unsuccessful in removing deleterious impurities from the water for reuse in all parts of the process. In the past an abundance of water at low cost more than excused this inefficiency. However, in light of recent shortfalls in supply, and ever increasing population and industrial demands on water such inefficiency can no longer be sanctioned.